Waveform equalization apparatus

ABSTRACT

A waveform equalization apparatus is provided with plural TF (transversal filter) units and plural selectors, and the TF units are connected such that the construction of the whole filter becomes a real component filter when an input signal is a VSB signal while it becomes a complex filter when the input signal is a QAM signal, by switching the inputs of each selector. The waveform equalization apparatus so constructed can waveform-equalize both the VSB signal and the QAM signal, and the circuit scale of the apparatus is reduced.

FIELD OF THE INVENTION

The present invention relates to a waveform equalization apparatus forreducing transmission line distortion of a digital signal which is usedfor digital broadcasting.

BACKGROUND OF THE INVENTION

Although digital broadcasting has initially been carried out mainly insatellite broadcasting, a tide of digitization recently rushes intoterrestrial broadcasting and cable broadcasting. A waveform equalizationtechnique for reducing transmission line distortion is indispensable forterrestrial digital broadcasting and cable digital broadcasting.

Hereinafter, a conventional waveform equalization apparatus forterrestrial digital broadcasting will be described taking, as anexample, a DTV (Digital Television) system using an 8-VSB (8-levelVestigial Side Band) modulation method that is adopted in the UnitedStates.

FIG. 11 is a block diagram illustrating a conventional waveformequalization apparatus adapted to the VSB modulation method. In FIG. 11,the waveform equalization apparatus is provided with a data inputterminal 1001 to which a DTV signal S1 employing the VSB modulationmethod (hereinafter referred to as a VSB signal) is applied; a digitalfilter unit 1015 for performing a filtering process, for waveformequalization on the VSB signal inputted from the data input terminal1001; a data output terminal 1011 for outputting the VSB signal S2 whichhas been subjected to the waveform equalization filtering process by thedigital filter unit 1015; and a tap coefficient control unit 1014 forcalculating tap coefficients to be used in the digital filter unit 1015on the basis of the data obtained from the digital filter unit 1015, andoutputting the tap coefficients to the digital filter unit 1015.

In the digital filter unit 1015, a 32-tap transversal filter(hereinafter referred to as a TF) 1002 receives the signal S1 applied tothe data input terminal 1001, and calculates a product of a signalobtained from each of the internal 32 taps and the corresponding tapcoefficient which is given by the tap coefficient control unit 1014, andoutputs the sum of products so calculated, as a signal obtained by afiltering process for waveform equalization, to an adder 1009 and,further, outputs a delay signal which is obtained by delaying the inputsignal, to the 32-tap TF 1003 and the adder 1009. The TF 1003 receivesthe delay signal outputted from the TF 1002, calculates a product of asignal obtained from each of the internal 32 taps and the correspondingtap coefficient which is given by the tap coefficient control unit 1014,and outputs the sum of products so calculated, as a signal obtained by afiltering process for waveform equalization, to the adder 1009. The TF1002 and the TF 1003 are used as an equivalent to a 64-tap TF, and thedelay signal outputted from the TF 1002 to the adder 1009 is regarded asa signal from a center tap of the 64-tap TF constituted by the TF 1002and the TF 1003, i.e., a main signal component. A delay unit 1004 delaysthe signal outputted from the adder 1009 by 32 symbols, and outputs thedelayed signal to a delay unit 1010 and a slicer 1005. The slicer 1005maps the output signal from the delay unit 1004 to a closest value amongthe eight values the VSB signal can take, thereby removing an influenceof noise of the input signal on the subsequent processes. A 64-tap TF1006 receives the signal outputted from the slicer 1005, calculates aproduct of a signal obtained from each internal tap and thecorresponding tap coefficient given by the tap coefficient control unit1014, and outputs the sum of products so calculated, as a signalobtained by a filtering process for waveform equalization, to the adder1009, and further, outputs a delay signal which is, obtained by delayingthe input signal to a 64-tap TF 1007. The 64-tap TF 1007 receives thesignal outputted from the TF 1006, calculates a product of a signalobtained from each internal tap and the corresponding tap coefficientgiven by the tap coefficient control unit 1014, and outputs the sum ofproducts so calculated, as a signal obtained by a filtering process forwaveform equalization, to the adder 1009, and further, outputs a signalwhich is obtained by delaying the input signal to a 64-tap TF 1008. The64-tap TF 1008 receives the signal outputted from the TF 1007,calculates a product of a signal obtained from each of the internal 64taps and the corresponding tap coefficient given by tap coefficientcontrol unit 1014, and outputs the sum of products so calculated, as asignal obtained by a filtering process for waveform equalization, to theadder 1009. The three TFs 1006, 1007, and 1008, which are connected inseries, are used instead of a 192-tap TF. The delay unit 1010 delays thesignal obtained from the delay unit 1004 by 192 symbols (−64 symbols×3),i.e., by symbols to be delayed by the TF 1006, TF 1007, and TF 1008, andoutputs the delayed signal to the tap coefficient control unit 1014. Theadder 1009 adds the results of the product-sum operations which arerespectively obtained from the TF 1002, TF 1003, TF 1006, TF 1007, andTF 1008 (i.e., signals obtained by the waveform equalization filteringprocesses of the respective TFs), and outputs a signal obtained by theaddition, as a waveform-equalized VSB signal S2, from the data outputterminal 1011 and, further, outputs the signal obtained by the addition,to the tap coefficient control unit 1014 and the delay unit 1004. Thotap coefficient control unit 1014 calculates the tap coefficientscorresponding to the respective taps included in the TF 1002, TF 1003,TF 1006, TF 1007, and TF 1008, on the basis of the outputs from theadder 1009 and the delay unit 1010, and outputs the tap coefficients tothe TF 1002, TF 1003, TF 1006, TF 1007, and TF 1008, thereby controllingupdation of the tap coefficients.

FIG. 12 is a diagram illustrating the structure of a VSB system signalformat. The VSB system signal format comprises an area including a datasignal 3101 such as video and audio data, an area including a field syncsignal 3102, and an area including a segment sync signal 3103.

FIG. 13 is a schematic diagram illustrating the structure of the fieldsync signal. With reference to FIG. 13, the field sync signal in thearea 3102 includes a PN 511 signal 3201, three PN 63 signals 3202, and acontrol signal 3203. In FIG. 12, a field sync signal #2 is differentfrom a field sync signal #1 only in that the second value of the PN 63signal 3202 is inverted. Further, in FIG. 13, numeric values on the leftside, i.e., +7, +5, +3, +1, −1, −3, −5, and −7, are examples of eightvalues the 8-VSB modulation method can take.

The VSB signal comprises 832 symbols and 313 segments per frame.Further, the PN 511 signal 3201 is represented byPN511=X⁹+X⁷+X⁶+X⁴+X³|X|1, and Pre-load is represented by 010000000. ThePN 63 signal 3202 is represented by PN 63=X⁶+X+1, and Pre-load isrepresented by 100111. The PN 511 signal 3201 comprises 511 symbols, thePN 63 signal 3202 comprises 63 symbols, and the control signal 3203comprises 128 symbols. Therefore, the whole field sync signal 3102comprises 828 symbols.

Next, the operation of the waveform equalization apparatus will bedescribed with reference to FIG. 11.

Initially, when an 8-VSB-modulated DTV signal is inputted to the datainput terminal 1001 as an input signal S1, the signal S1 is subjected toa waveform equalization process by the TF 1002 and the TF 1003 on thebasis of the tap coefficients which are set by the tap coefficientcontrol unit 1014, and the result of product-sum operation performed onthe outputs from the internal taps of each of the TF 1002 and TF 1003,as well as a delay signal outputted from the TF 1002, are transmitted tothe adder 1009. The adder 1009 sums the inputted signals, and outputsthe resultant signal from the data output terminal 1011 as an outputsignal S2, and further, outputs the signal to the tap coefficientcontrol unit 1014 and the delay unit 1004. The delay unit 1004 delaysthe output signal S2 by 32 symbols and outputs the delayed signal to theslicer 1005 and the delay unit 1010. The slicer 1005 maps the output ofthe delay unit 1004 to a closest value among the eight values, therebyremoving an influence of noise of the signal on the subsequentprocesses. Each of the TF 1006, TF 1007, and TF 1008 waveform-equalizesthe output of the slicer 1005, and outputs the result to the adder 1009.The delay unit 1010 delays the output of the delay unit 1004 by 192symbols, i.e., by symbols to be delayed by the TF 1006, TF 1007, and TF1008, and outputs the delayed signal to the tap coefficient control unit1014. The delay unit 1010 is provided for outputting the output of thedelay unit 1004 which is not octal-leveled by the slicer 1005, to thetap coefficient control unit 1014. The tap coefficient control unit 1014obtains a difference between the output signal S2 and a most reliablesymbol value among the eight symbol values shown in FIG. 13, andperforms updation of the tap coefficients of the TF 1002, TF 1003, TF1006, TF 1007, and TF 1008, using the difference, on the basis of theLMS (Least Mean Square) algorithm.

As described above, the TF 1002 and the TF 1003 function in a similarmanner to a single TF, and these TFs serve as a so-called feed-forwardtype TF. Further, the TF 1006, TF 1007, and TF 1008 also function in asimilar manner to a single TF, and these TFs serve as a so-calledfeed-back type TF, which performs waveform equalization on the signalthat is 32 symbols delayed by the delay unit 1004, thereby to realizewaveform equalization on the rear region which cannot bewaveform-equalized by the TFs 1002 and 1003.

Next, the operation of the tap coefficient control unit 1014 will bedescribed. The tap coefficient control unit 1014 obtains a differencebetween the inputted output signal S2 and the most reliable symbol valueamong the eight symbol values, and performs updation of the tapcoefficients of the TF 1002, TF 1003, TF 1006, TF 1007, and TF 1008 onthe basis of the LMS algorithm. The LMS algorithm is an algorithm forperforming the n-th updation (n: positive integer) of a tap coefficientCi of a tap i (i: positive integer) in any of the TF 1002, TF 1003, TF1006, TF 1007, and TF 1008 on the basis of the following formula (1).Ci(n+1)=Ci(n)−α×en×di  (1)where α indicates a fixed constant step size for deciding a coefficientupdation amount, en is an error in the output signal, di indicates dataof the tap i, and −α×en×di indicates the coefficient updation amount.The tap coefficient control unit 1014 updates the tap coefficients to beused in the TF 1002, TF 1003, TF 1006, TF 1007, and TF 1008 on the basisof formula (1). The output signal S2 is represented by the followingformula (2).S 2(n)−Σ(i=0, 255)(Ci(n)×di)  (2)

Next, a description will be given of a conventional waveformequalization apparatus used for cable digital broadcasting. Also incable digital broadcasting, waveform equalization using the LMSalgorithm is carried out. However, cable digital broadcasting usuallyemploys, as a modulation method, not the 8-VSB modulation method but aQAM (Quadrature Amplitude Modulation) method.

FIG. 14 shows an arrangement of signal points, with respect to a DTVsignal using a 64-state QAM method (hereinafter referred to as a 64-QAMsignal). In FIG. 14, the abscissa shows the real number axis while theordinate shows the imaginary number axis.

FIG. 15 is a block diagram illustrating a waveform equalizationapparatus adapted to the 64-state QAM method. With reference to FIG. 15,a real component of a 64-QAM signal is inputted to a data input terminal2001. The inputted real component of the 64-QAM signal is inputted to aTF 2003 and a TF 2005. The TF 2003 performs a product-sum operation ofthe outputs from the respective internal taps, and outputs the result asa signal obtained by a filtering process for waveform equalization, to asubtracter 2007. Further, a main signal of the TF 2003 is inputted to anadder 2009. Further, the outputs from the respective taps of the TF 2003are inputted to a tap coefficient control unit 2013. The TF 2005performs a product-sum operation of the outputs from the respectiveinternal taps, and outputs the result to an adder 2008 as a signalobtained by a filtering process for waveform equalization.

On the other hand, an imaginary component of the 64-QAM signal isinputted to a data input terminal 2002. Then, the imaginary component ofthe 64-QAM signal is inputted to a TF 2004 and a TF 2006. The TF 2006performs a product-sum operation of the outputs from the respectiveinternal taps, and outputs the results to the adder 2008 as a signalobtained by a filtering process for waveform equalization. Further, amain signal of the TF 2006 is inputted to an adder 2010. Furthermore,the outputs from the respective taps of the TF 2006 are inputted to thetap coefficient control unit 2013. The TF 2004 performs a product-sumoperation of the outputs from the respective internal taps, and outputsthe result to the subtracter 2007 as a signal obtained by a filteringprocess for waveform equalization.

The subtracter 2007 subtracts the output of the product-sum operationresult of the TF 2004 from the output of the product-sum operationresult of the TF 2003. The adder 2009 adds the output of the subtracter2007 and the main signal of the TF 2003, and outputs the sum as a realcomponent of a complex output signal S22 from the data output terminal2001 and, further, inputs the sum to the tap coefficient control unit2013.

The adder 2008 adds the output of the product-sum operation result ofthe TF 2006 and the output of the product-sum operation result of the TF2005. The adder 2010 adds the output of the adder 2008 and the mainsignal of the TF 2006, and outputs the sum as an imaginary component ofthe complex output signal S22 from the data output terminal 2012 and,further, inputs the sum to the tap coefficient control unit 2013. Thetap coefficient control unit 2013 controls updation of the tapcoefficients of the TFs 2003˜2006, on the basis of the real componentand imaginary component of the complex output signal S22.

The complex output signal S22 obtained from the waveform equalizationapparatus is represented by the following formula (3).S 22(n)=Σ(i=0, 255)(Ci(n)×di)  (3)

In formula (3), when Ci(n) and di are represented by complex elements asfollows:Di−di(r)+jdi(i)Ci(n)=Ci(n)(r)+jCi(n)  (i)where (r) indicates real component data, and (i) indicates imaginarycomponent data, the complex output signal S22 is represented as follows:S 22(n)=Σ(i=0, 255)((Ci(n)(r)+jCi(n)(i))×(di(r)+jdi(i))) =Σ(i=0,255)((Ci(n)(r)×di(r)−Ci(n)(i)×di(i))+j(Ci(n)(r)×di(i)+Ci(n)(i)×di(r)))

When S22(n) is represented byS 22(n)=S 22(n)(r)+jS 22(n)(i)S22(n)(r) and JS22(n)(i) are represented by the following formulae (4)and (5), respectively.S 22(n)(r)=Σ(i−0, 255)(Ci(n)(r)×di(r)−Ci(n)(i)×di(i))  (4)S 22(n)(i)=Σ(i=0, 255)(Ci(n)(r)×di(i)+Ci(n)(i)×di(r))  (5)

Next, the tap coefficient updating operation by the tap coefficientcontrol unit 2013 will be described.

The tap coefficient control unit 2013 controls updation of the tapcoefficients of the TFs 2003˜2006 on the basis of the real component andimaginary component of the inputted complex output signal S22 as well asthe tap outputs from the TF 2003 and the TF 2006. A tap coefficientupdation formula to be used in the case where a QAM signal is inputtedis represented as follows, using the LMS algorithm, in a similar mannerto the above-mentioned formula (1).Ci(n+1)−Ci(n)−α×en×di*  (6)where di* indicates the complex conjugate (complex number) of di.

When formula (6) is developed using complex expressions as follows:Ci(n)−Ci(n)(r)+jCi(n)(i)en=en(r)+jen(i)di=di(r)+jdi(i) di*=di(r)−jdi(i)the real component is represented byCi(n+1)(r)=Ci(n)(r)−α×{en(r)×di(r)+en(i)×di(i)}and the imaginary component is represented byCi(n+1)(i)=Ci(n)(i)−α×{en(i)×di(r)+en(r)×di(i)}

The conventional waveform equalization apparatuses are constituted asdescribed above, and a DTV signal with reduced distortion can beobtained by employing these waveform equalization apparatuses.

In the conventional waveform equalization apparatuses, however, thecalculation of the output signal varies between the case where the VSBsignal is inputted and the case where the QAM signal is inputted, asshown by formula (2) for the VSB signal and formulae (4) and (5) for theQAM signal, and therefore, separated waveform equalizers adapted to therespective signals must be prepared. Accordingly, when providing awaveform equalization apparatus adaptable to both of the VSB signal andthe QAM signal, waveform equalizers adapted to the respective signalsare required and these equalizers should be switched according to theinput signal, resulting in an increase in the circuit scale.

Furthermore, the tap coefficient control unit 1014 calculates the tapcoefficients using an error in the VSB signal, according to the LMSalgorithm as shown by formula (1). Therefore, the signal before beingsliced by the slicer 1005 must be delayed by a time equal to the time tobe delayed by the TF 1006, TF 1007, and TF 1008, before it is inputtedto the tap coefficient control unit 1014, and the delay unit 1010 isrequired as means for delaying the signal. However, such delay unit islarge in circuit scale, resulting in an increase in the circuit scale ofthe whole waveform equalization apparatus.

Furthermore, in the conventional waveform equalization apparatus,adaptive control for optimizing the filter characteristic is carried outby updating the tap coefficients with the tap coefficient control unit1014 on the basis of the output signal. Therefore, the filtercharacteristic is not constant but varies with the updation of the tapcoefficients. As a result, it is difficult for the user to know thefilter characteristic that is updated by the adaptive control.

SUMMARY OF THE INVENTION

The present invention is made to solve the above-described problems andhas for its object to provide a waveform equalization apparatus which isable to perform waveform equalization on both of a VSB signal and a QAMsignal, has a reduced circuit scale, and enables the user to easily knowthe filter characteristic that is updated by adaptive control.

Other objects and advantages of the invention will become apparent fromthe detailed description that follows. The detailed description andspecific embodiments described are provided only for illustration sincevarious additions and modifications within the scope of the inventionwill be apparent to those of skill in the art from the detaileddescription.

According to a first aspect of the present invention, there is provideda waveform equalization apparatus comprising: a first input terminal towhich only a real component of a digital input signal to bewaveform-equalized is applied; a second input terminal to which only animaginary component of the digital input signal to be waveform-equalizedis applied; plural transversal filters for performing filteringprocesses for waveform equalization on the digital input signal; a firstoutput terminal from which only a real component of a waveform-equalizeddigital output signal is outputted; a second output terminal from whichonly an imaginary component of the waveform-equalized digital outputsignal is outputted; plural selectors for selecting a connection oflines which interconnect the first or second input terminal, the pluraltransversal filters, and the first or second output terminal; and afilter construction control signal generator for generating a filterconstruction control signal which controls the plural selectors tocontrol the filter construction such that the whole apparatus becomes areal component filter when the digital input signal is a signal havingonly a real component, and becomes a complex filter when the digitalinput signal is a signal leaving both a real component and an imaginarycomponent.

According to a second aspect of the present invention in the generatinga filter operation control signal which changes the filter operation bychanging the tap length of the predetermined transversal filter.

According to a sixth aspect of the present invention, there is provideda waveform equalization apparatus comprising a first input terminal towhich a digital input signal having only a real component is inputted; asecond input terminal to which a digital input signal having only animaginary component is inputted; first and second output terminals;first to fourth transversal filter (hereinafter referred to as TF) unitsfor performing filtering processes for waveform equalization; a delaymeans for delaying an input signal to output a delayed signal; and firstand second tap coefficient control means for controlling tapcoefficients of the first to fourth TF units; wherein, when a signal isapplied to only the first input terminal, the first to fourth TF unitsare connected as follows: the signal applied to the first input terminalis inputted to the first TF unit; a signal which is obtained by delayinga signal outputted from the first output terminal with the delay meansis inputted to the second TF unit; a delay output from the second TFunit is inputted to the third TF unit; a delay output from the third TFunit is inputted to the fourth TF unit; and signals which arefilter-processed by the second to fourth TF units are added to a signalwhich is filter-processed by the first. TF unit and a main signalcomponent of the first TF unit, and the result of the addition isoutputted from the first output terminal; and waveform equalization isperformed on the input signal to the first input terminal whilecontrolling the tap coefficients of the first to fourth TF units withthe first tap coefficient control means on the basis of the output fromthe first output terminal, and a signal so obtained is outputted fromthe first output terminal; and when signals are applied to both of thefirst input terminal and the second input terminal, the first to fourthTF units are connected as follows: the signal applied to the first inputterminal is inputted to the first and third TF units; the signal appliedto the second input terminal is inputted to the second and fourth TFunits; the main signal component of the first TF unit is added to avalue which is obtained by subtracting the signal filter-processed bythe second TF unit from the signal filter-processed by the first TFunit, and the result of the addition is outputted from the first dataoutput terminal; and the signal filter-processed by the third TF unit,the signal filter-processed by the fourth TF unit, and the main signalcomponent of the fourth TF unit are added, and the result of theaddition is outputted from the second output terminal; and the inputsignals applied to the first and second input terminals are subjected towaveform equalization while controlling the tap coefficients of thefirst to fourth TF units with the second tap coefficient control meanson the basis of the outputs from the first and second output terminals,and the real component of the signal so obtained is outputted from thefirst output terminal while the imaginary component of the signal soobtained is outputted from the second output terminal.

According to a seventh aspect of the present invention, in the waveformequalization apparatus according to the sixth aspect, each of the firstand fourth TF units is provided with n pieces of TFs (n: integer equalto or larger than 3), and the respective TFs are connected such that adelay output from the m-th TF (1≦m≦n−1, m: integer) is inputted to the(m+1)th TF; and the waveform equalization apparatus further includes: afirst selection means for receiving delay outputs from the first to(n−1)th TFs of the first TF unit, respectively, selecting one of theplural delay outputs on the basis of a center tap control signal that issupplied from the outside, and outputting the selected signal as a mainsignal component of the first TF unit; and a second selection means forreceiving delay outputs from the first to (n−1)th TFs of the fourth TFunit, respectively, selecting one of the plural delay outputs on thebasis of the center tap control signal, and outputting the selecteddelay output as a main signal component of the fourth TF unit.

According to an eighth aspect of the present invention, in the waveformequalization apparatus according to the sixth aspect, at least one ofthe first to fourth TF units is provided with n pieces of TFs (n:integer equal to or larger than 2), and the respective TFs are connectedsuch that a delay output from the m-th TF (1≦m≦n−1, m: integer) isinputted to the (m+1)th TF, and the operating state of at least one ofthe TFs is switched between the active state and the halt state by afilter operation control signal that is supplied from the outside.

According to a ninth aspect of the present invention, in the waveformequalization apparatus according to the sixth aspect, each of the firstand fourth TF units is provided with n pieces of TFs (n: integer equalto or larger than 2), and the respective TFs are connected such that adelay output from the m-th TF (1≦m≦n−1, m: integer) is inputted to the(m+1)th TF; each of the second and third TF units is provided with spieces of TFs (s: integer equal to or larger than 2), and the respectiveTFs are connected such that a delay output from the t-th TF (1≦t≦s−1, t:integer) is inputted to the (t+1)th TF; and the operating state of atleast one TF among the plural TFs constituting each of the first tofourth TF units is switched between the active state and the halt stateby a filter operation control signal that is supplied from the outside.

According to a tenth aspect of the present invention, there is provideda waveform equalization apparatus comprising: a first input terminal towhich a digital input signal having only a real component is applied; asecond input terminal to which a digital input signal having only animaginary component is applied; a first TF unit for receiving the inputsignal applied to the first input terminal, and outputting a signalwhich is subjected to a filtering process for waveform equalization, anda main signal component in the filtering process; a first selectioncircuit having first and second inputs, receiving, as the second input,the input signal applied to the second input terminal, and selectingeither of the first and second inputs to output the selected input; asecond TF unit for receiving the output of the first selection circuit,and outputting a signal which is subjected to a filtering process forwaveform equalization, and a delay signal obtained by delaying the inputsignal; a second selector for selecting either the input signal appliedto the first input terminal or the delay signal outputted from thesecond TF unit, and outputting the selected signal; a third TF unit forreceiving the output of the second selection circuit, and outputting asignal which is subjected to a filtering process for waveformequalization, and a delay signal obtained by delaying the input signal;a third selector for selecting either the input signal applied to thesecond input terminal or the delay signal outputted from the third TFunit, and outputting the selected signal; a fourth TF unit for receivingthe output of the third selection circuit, and outputting a signal whichis subjected to a filtering process for waveform equalization, and amain signal component in the filtering process; a fourth selector forselecting either the signal obtained by the filtering process in thesecond TF unit or a signal obtained by inverting the filter-processedsignal, and outputting the selected signal; a fifth selector forselecting either a signal which is obtained by adding the output of thefourth selector and the signal obtained by the filtering process in thefirst TF unit, or the main signal component outputted from the fourth TFunit, and outputting the selected signal; a sixth selector for selectingeither a signal which is obtained by adding the output of the fourthselector and the signal obtained by the filtering process in the firstTF unit, or a signal which is obtained by adding the signal obtained bythe filtering process in the third TF unit and the signal obtained bythe filtering process in the fourth TF unit, and outputting the selectedsignal; a first output terminal for outputting a signal which isobtained by adding the output of the sixth selector and the main signalcomponent of the first TF unit; a delay unit for delaying a signal whichis obtained by adding the output of the sixth selector and the mainsignal component of the first TF unit, and outputting the delayed signalso that it becomes a first input to the first selector; a second outputterminal for outputting a signal which is obtained by adding the outputof the fifth selector, the signal obtained by the filtering process inthe third TF unit, and the signal obtained by the filtering process inthe fourth TF unit; a first tap coefficient control means forcontrolling the tap coefficients of the first to fourth TF units, on thebasis of a signal which is obtained by adding the output of the sixthselector and the main signal component of the first TF unit; and asecond tap coefficient control means for controlling the tapcoefficients of the first to fourth TF units, on the basis of the signalwhich is obtained by adding the output of the sixth selector and themain signal component of the first TF unit, as well as the signal whichis obtained by adding the output of the fifth selector, the signalobtained by the filtering process in the third TF unit, and the signalobtained by the filtering process in the fourth TF unit; wherein, when asignal is inputted to only the first input terminal, the first selectorselects the input from the delay unit and outputs it; the secondselector selects the delay signal from the second TF unit and outputsit; the third selector selects the delay signal from the third TF unitand outputs it; the fourth selector selects the signal which is obtainedby the filtering process in the second TF unit, and outputs it; thefifth selector selects the signal which is obtained by adding the outputof the fourth selector and the signal obtained by the filtering processin the first TF unit, and outputs it; the sixth selector selects thesignal which is obtained by adding the output of the fifth selector, thesignal obtained by the filtering process in the third TF unit, and thesignal obtained by the filtering process in the fourth TF unit, andoutputs it; and the first tap coefficient control means controls the tapcoefficients of the first to fourth TF units; and when signals areinputted to both of the first input terminal and the second inputterminal, the first selector selects the input of the second inputterminal and outputs it; the second selector selects the input of thefirst input terminal and outputs it; the third selector selects theinput of the second input terminal and outputs it; the fourth selectorselects an inverted signal of the signal which is obtained by thefiltering process in the second TF unit, and outputs it; the fifthselector selects the main signal component of the fourth TF unit andoutputs it; the sixth selector selects the signal which is obtained byadding the output of the fourth selector and the signal obtained by thefiltering process in the first TF unit, and outputs it; and the firsttap coefficient control means controls the tap coefficients of the firstto fourth TF units.

According to an eleventh aspect of the present invention, in thewaveform equalization apparatus according to the tenth aspect, each ofthe first and fourth TF units is provided with n pieces of TFs (n:integer equal to or larger than 3), and the respective TFs are connectedsuch that a delay output from the m-th TF (1≦m≦n−1, m: integer) isinputted to the (m+1)th TF, and a signal which is obtained by adding thesignals that are filter-processed by the respective TFs is outputted asa filter-processed output from each of the first and fourth TF units;and the waveform equalization apparatus further includes: a seventhselection means for receiving delay outputs from the first to (n−1)thTFs of the first TF unit, respectively, selecting one of the pluraldelay outputs on the basis of a center tap control signal that issupplied from the outside, and outputting the selected signal as a mainsignal component of the first TF unit; and an eighth selection means forreceiving delay outputs from the first to (n−1)th TFs of the fourth TFunit, respectively, selecting one of the plural delay outputs on thebasis of the center tap control signal, and outputting the selectedsignal as a main signal component of the fourth TF unit.

According to a twelfth aspect of the present invention, in the waveformequalization apparatus according to the tenth aspect, at least one ofthe first to fourth TF units is provided with n pieces of TFs (n:integer equal to or larger than 2), and the respective TFs are connectedsuch that a delay output from the m-th TF (1≦m≦n−1, m: integer) isinputted to the (m+1)th TF, and the operating stale of at least one ofthe TFs is switched between the active state and the halt state by afilter operation control signal that is supplied from the outside.

According to a thirteenth aspect of the present invention, in thewaveform equalization apparatus according to the tenth aspect, each ofthe first and fourth TF units is provided with n pieces of TFs (n:integer equal to or larger than 2), and the respective TFs are connectedsuch that a delay output from the m-th TF (1≦m≦n−1, m: integer) isinputted to the (m+1)th TF; each of the second and third TF units isprovided with s pieces of TFs (s: integer equal to or larger than 2),and the respective TFs are connected such that a delay output from thet-th TF (1≦t≦s−1, t: integer) is inputted to the (t+1)th TF; and theoperating state of at least one TF among the plural TFs constitutingeach of the first to fourth TF units is switched between the activestate and the halt state by a filter operation control signal that issupplied from the outside.

According to a fourteenth aspect of the present invention, there isprovided a waveform equalization apparatus comprising: an input terminalto which a digital input signal having only a real component is applied;a first TF for performing a waveform equalization filtering process onthe input signal applied to the input terminal; an adder for receiving,as one of plural inputs, the filter-processed output from the first TF,and adding the inputted signals to output the result of the addition; anoutput terminal for outputting the output of the adder; a delay unit fordelaying the output of the adder, and outputting the delayed signal; aslicer for slicing the output of the delay unit; a second TF forperforming a waveform equalization filtering process on the output ofthe slicer, inputting the filter-processed signal to the adder, andoutputting a delay output obtained by delaying the output of the slicer,and signals obtained from the respective taps; a third TF for performinga waveform equalization filtering process on the delay output of thesecond TF, inputting the filter-processed signal to the adder, andoutputting a delay output obtained by delaying the delay output of thesecond TF, and signals obtained from the respective taps; a fourth TFfor performing a waveform equalization filtering process on the delayoutput of the third TF, inputting the filter-processed signal to theadder, and outputting signals obtained from the respective taps; and atap coefficient control means for controlling the tap coefficients ofthe first to fourth TFs on the basis of the output of the adder, and thesignals obtained from the respective taps of the second to fourth TFs.

According to a fifteenth aspect of the present invention, there isprovided a waveform equalization apparatus comprising: an input terminalto which a digital signal is applied; a test signal generator forgenerating a signal for test; an input signal selection means forselecting either the signal applied to the input terminal or the lostsignal, on the basis of a mode input signal that is supplied from theoutside; a digital filter unit having at least one TF, and performing afiltering process for waveform equalization on the signal that isselected by the input signal selection means; an output terminal foroutputting the signal that is filter-processed by the digital filterunit; and a tap coefficient control means for updating the tapcoefficient of the TF in the digital filter unit on the basis of thesignal that is filter-processed by the digital filter unit when theinput signal selection means selects the signal applied to the inputsignal, and performing no updation of the tap coefficient when the inputsignal selection means selects the test signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the construction of a waveformequalization apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a diagram for explaining the operation of the waveformequalization apparatus according to the first embodiment, in the casewhere a VSB signal is inputted to the apparatus.

FIG. 3 is a diagram for explaining the operation of the waveformequalization apparatus according to the first embodiment, in the casewhere a QAM signal is inputted to the apparatus.

FIG. 4 is a block diagram illustrating a waveform equalization apparatusaccording to a second embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of the waveformequalization apparatus according to the second embodiment in the casewhere a VSB signal is inputted to the apparatus.

FIG. 6 is a diagram for explaining the operation of the waveformequalization apparatus according to the second embodiment in the casewhere a QAM signal is inputted to the apparatus.

FIG. 7 in a block diagram illustrating a waveform equalization apparatusaccording to a third embodiment of the present invention.

FIG. 8 is a diagram for explaining the operation of the waveformequalization apparatus according to the third embodiment in the casewhere a QAM signal is inputted to the apparatus.

FIG. 9 is a diagram illustrating a waveform equalization apparatusaccording to a fifth embodiment of the present invention.

FIG. 10 is a block diagram illustrating a waveform equalizationapparatus according to a fourth embodiment of the present invention.

FIG. 11 is a block diagram illustrating an example of a conventionalwaveform equalization apparatus to be used for waveform equalization ofa VSB signal.

FIG. 12 is a diagram illustrating the construction of a signal format ofa VSB signal.

FIG. 13 is a diagram illustrating the construction of a field syncsignal included in the VSB signal.

FIG. 14 is a diagram illustrating an arrangement of signal points of aQAM signal.

FIG. 15 is a block diagram illustrating an example of a waveformequalization apparatus to be used for waveform equalization of a QAMsignal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 1 is a block diagram illustrating a waveform equalization apparatusaccording to a first embodiment of the present invention. With referenceto FIG. 1, a 32-tap TF 101 included in a transversal filter unit(hereinafter referred to as a TF unit) 101 a receives an input signalapplied to a data input terminal 1, calculates products of outputs fromplural internal taps (not shown) and tap coefficients corresponding tothe respective taps, sums the products so obtained, and outputs theresult of the product-sum operation, as a result of a filtering processfor waveform equalization, to an adder 113. Further, the 32 tap TF 101delays the input signal using an internal delay circuit (not shown), andoutputs a delay signal so obtained to a 32-tap TF 102 and an adder 118.The 32-tap TF 102 included in the TF unit 101 a receives the delaysignal outputted from the TF 101, and outputs a result of a product-sumoperation which is obtained by summing up the products of outputs fromplural internal taps (not shown) and the tap coefficients correspondingto the respective taps, as a result of a filtering process, to the adder113. The TF unit 101 a is equivalent to a 64-tap TF, and the delaysignal outputted from the TF 101 to the adder 118 serves as a mainsignal component of the TF unit 101 a. In this first embodiment, a64-tap TF may be employed instead of the TF unit 101 a comprising the TF101 and the TF 102. The adder 113 adds the delay signal outputted fromthe TF 101 and the TF 102, and outputs the sum to an adder 115.

A selector 107, having first and second inputs, receives the inputsignal applied to the data input terminal as the second input, selectseither the first input or the second input, and outputs the selected oneto a TF unit 103 a. A 64-tap TF 103 as a component of the TF unit 103 aoutputs a result of a product-sum operation which is performed on theoutputs from the respective internal taps and the corresponding tapcoefficients, as a result of a filtering process, to a selector 110 anda code inverter 119 and, further, outputs a delay signal to a selector108. The selector 108 selects either the delay signal from the TF unit103 a or the input signal from the data input terminal 1, and outputsthe selected signal to a TF unit 104 a. A 64-tap TF 104 as a componentof the TF unit 104 a outputs a result of a product-sum operation whichis performed on the outputs of the respective internal taps and thecorresponding tap coefficients, as a result of a filtering process, toan adder 116, and further, outputs a delay signal to a selector 109.

The selector 109 selects either the input signal from the data inputterminal 120 or the delay signal from the TF unit 104 a, and outputs theselected signal to a TF unit 105 a. A 32-tap TF 105 as a constituent ofthe TF unit 105 a receives the output of the selector 109, and outputs aresult of a product-sum operation which is obtained by summing up theproducts of the outputs from the plural internal taps and the tapcoefficients corresponding to the respective taps, as a result of afiltering process, to an adder 114, and further, outputs a delay signalto a TF 106 and a selector 111. Further, the 32-tap TF 106 as acomponent of the TF unit 105 a receives the delay signal from the TF105, and outputs a result of a product-sum operation which is obtainedby summing up the products of the outputs from the plural internal tapsand the tap coefficients corresponding to the respective taps, as aresult of a filtering process, to the adder 114. The TF unit 105 a isequivalent to a 64-tap TF, and the delay signal outputted from the TF105 to the selector 111 serves as a main signal component of the TF unit105 a. In this first embodiment, a 64-tap TF may be employed instead ofthe TF unit 105 a comprising the TF 105 and the TF 106.

The adder 114 output a signal obtained by adding the results of theproduct-sum operations from the TF 105 and the TF 106, to the adder 116.The adder 116 adds the output from the adder 114 and the result of theproduct-sum operation from the TF 104, and outputs the sum to an adder117. The code inverter 119 receives the result of the product-sumoperation outputted from the TF unit 103 a, and outputs a signalobtained by inverting the codes of the input signal, to the selector110. The selector 110 selects either the output of the code inverter 119or the result of the product-sum operation from the TF unit 103 a, andoutputs the selected one to the adder 115. The adder 115 adds the outputfrom the selector 110 and the output from the adder 113, and outputs asignal obtained by the addition to the selectors 112 and 111. Theselector 111 selects either the delay signal from the TF 105 in the TFunit 105 a (i.e., the main signal component of the TF unit 105 a) or theoutput from the adder 115, and outputs the selected one to the adder117. The adder 117 adds the output of the selector 111 and the output,of the adder 116, and outputs a signal obtained by the addition, as anoutput signal, from the data output terminal 121, and further, outputsthe signal to the selector 112 and a tap coefficient controller 150. Theselector 112 selects either the output of the adder 117 or the output ofthe adder 115, and outputs the selected one to the adder 118. The adder118 adds the output of the selector 112 and the delay signal from the TF101 in the TF unit 101 a (i.e., the main signal component of the TF unit101 a), and outputs a signal obtained by the addition, as an outputsignal, from the data output terminal 11, and further, outputs thesignal to a tap coefficient controller 140, the tap coefficientcontroller 150, and a delay unit 4.

The delay unit 4 delays the output signal from the adder 118 by 32symbols, and outputs the delayed signal to a slicer 5 and a value amongplural values the VSB signal can take (in this case, eight values), andinputs the mapped value to the selector 107 as a first input. The delayuntil 130 delays the output signal from the delay unit 4 by 192 symbols,and outputs the delayed signal to the tap coefficient controller 140.The tap coefficient controller 140 receives the output signal to beoutputted from the data output terminal 11, and the output from thedelay unit 130, obtains differences between these signals and a mostreliable symbol among the eight kinds of symbol values, obtains tapcoefficients to be used in the TFs 101˜106, using the differences soobtained, on the basis of the LMS algorithm, and transmits controlsignals (not shown) to the TFs 101˜106, thereby updating the respectivetap coefficients to be used in the TFs 101˜106 with the obtained tapcoefficients. The tap coefficient controller 150 receives the outputsignal from the data output terminal 11, the output signal from the dataoutput terminal 121, the signals obtained from the respective taps inthe TF unit 101 a, and the signals obtained from the respective taps inthe TF unit 105 a, and obtains differences between these signal and amost reliable symbol value among the symbol values the QAM signal cantake, obtains tap coefficients to be used in the TFs 101˜106 on thebasis of the LMS algorithm using these differences, and transmitscontrol signals (not shown) to the TFs 101˜106, thereby updating therespective tap coefficients to be used in the TFs 101˜106 with theobtained tap coefficients. A control signal for controlling theselectors 107˜112 is supplied to a filter construction control terminal122 from the outside. Each of the selectors 107˜112 is supplied with thecontrol signal, and each selector selects one of the two input signalsaccording to the control signal. That is, the control signal controlsswitching of the input signals. This control signal is previously storedin an external register or the like (not shown), and is inputted to thefilter construction control terminal 122, according to the signalinputted to the waveform equalization apparatus, on the basis of aninstruction from an external controller or the like (not shown).

FIG. 2 is a block diagram for explaining the operation of the waveformequalization apparatus according to the first embodiment in the casewhere a DTV signal having only a real component and employing the VSBmodulation method (hereinafter refereed to as a VSB signal) is inputtedto the apparatus. FIG. 2 is identical to FIG. 1 except that unusedsignal lines are shown by dotted lines. Hereinafter, a description willbe given of the operation of the waveform equalization apparatus in thecase where a 8-VSB signal is inputted to the apparatus, with referenceto FIG. 2.

First of all, a filter construction control signal for switching theinputs to each of the selectors 107˜112 in accordance with the VSBsignal, for example, “1”, is supplied from the outside to the filterconstruction control terminal 122, while a 8-VSB signal is inputted tothe data input terminal 1.

In the TF unit 101 a, the TF 101 performs a filtering process on the8-VSB signal inputted to the data input terminal 1, and outputs thefilter-processed signal to the adder 113, and outputs a delay signalwhich is obtained by delaying the input signal with the internal delaycircuit, to the TF 102. Further, the TF 101 outputs the delay signal tothe adder 118, as a main signal component of the TF unit 101 a. The TF102 performs a filtering process on the delay signal outputted from theTF 101, and outputs the filter-processed signal to the adder 113. Theadder 113 adds the filter-processed signals from the TF 101 and the TF102, and outputs the sum.

The selector 107 selects the output of the slicer 5 on the basis of thefilter construction control signal, and outputs it to the TF 103. The TF103 performs a filtering process on the output of the slicer, andoutputs the filter-processed signal, and further, outputs a delay signalwhich is obtained by delaying the signal with the internal delaycircuit. The selector 108 selects the delay signal outputted from the TF103, on the basis of the filter construction control signal, and outputsit to the TF 104. The TF 104 perform a filtering process on the delaysignal outputted from the TF 103, and outputs the filter-processedsignal and a delay signal. The selector 109 selects the delay signalfrom the TF 104, on the basis of the filter construction control signal,and outputs it to the TF unit 105 a.

In the TF unit 105 a, the TF 105 performs a filtering process on thedelay signal outputted from the TF 104, and outputs the filter-processedsignal to the adder 114, and outputs a delay signal to the TF 106. TheTF 106 performs a filtering process on the delay signal, and outputs thefilter-processed signal to the adder 114. In this way, the selectors107˜109 are controlled so as to perform signal selecting operations bythe filter construction control signal “1” which is inputted to thefilter construction control terminal 122, whereby the TF 103, the TF104, the TF 105, and the TF 106 are connected in series. That is, the TFunit 103 a, the TF unit 104 a, and the TF unit 105 a are connected inseries. The adder 114 adds the signal which is filter-processed by theTF 105 and the signal which is filter-processed by the TF 106, andoutputs the sum to the adder 116. The adder 116 adds the output of theadder 114 and the filter-processed signal obtained from the TF 104, andoutputs the sum to the adder 117.

The selector 110 selects the filter-processed signal outputted from theTF 103, on the basis of the filter construction control signal, andoutputs it to the adder 115. The adder 115 adds the output of theselector 110 and the output of the adder 113, and outputs the sum. Theselector 111 selects the output of the adder 115 on the basis of thefilter construction control signal, and supplies it to the adder 117.The adder 117 adds the output of the selector 111 and the output of theadder 116, and outputs the sum. The selector 112 selects the output ofthe adder 117, and supplies it to the adder 118. The adder 118 adds theoutput of the selector 112 and the delay signal from the TF 101 (i.e.,the main signal component of the TF unit 101 a), and outputs a signalobtained by the addition, from the data output terminal 11, as an outputsignal which is obtained by subjecting the VSB signal to waveformequalization. Further, the adder 118 outputs the signal to the delayunit 4 and the tap coefficient control circuit 140. The delay unit 4delays the output signal from the adder 118 to synchronize the timing ofthe filtering process by the TF unit 101 a with the timings of thefiltering processes by the TF unit 103 a, the TF unit 104 a, and the TFunit 105 a, and outputs the delayed signal to the slicer 5. In thisfirst embodiment, a signal obtained by delaying the output of the adder118 by 32 symbols is outputted to the slicer 5. The slicer 5 maps theoutput of the delay unit 4 to a closest value among the eight values theVSB signal can take. The delay unit 130 delays the output of the delayunit 4 by symbols to be delayed by the 64-tap TF unit 103 a, the 64-tapTF unit 104 a, and the 64-tap TF unit 105 a which are connected inseries, i.e., by 192 symbols, and output the delayed signal to the tapcoefficient control circuit 140. The tap coefficient control circuit 140obtains a difference between the output of the data output terminal 11(i.e., the output of the adder 118) and a most reliable symbol valueamong the eight symbol values, and a difference between the output ofthe delay unit 130 and the most reliable symbol value, and obtains tapcoefficients to be used in the TFs 101˜106 on the basis of the LMSalgorithm using these differences, and transmits a control signal whichinstructs updation of the tap coefficients to the TFs 101˜106, therebyupdating the tap coefficients.

In this way, as for the VSB signal comprising the real component, theTFs 101˜106 are constructed as real component filters by controlling theselectors 107˜112. That is, the TF unit 101 a is constructed as afeed-forward type TF, while the TF unit 103 a, the TF unit 104 a, andthe TF unit 105 a are constructed as feed-back type TFs connected inseries.

FIG. 3 is a block diagram for explaining the operation of the waveformequalization apparatus according to the first embodiment in the casewhere a DTV signal comprising a real component and an imaginarycomponent and employing the QAM method (hereinafter referred to as a QAMsignal) is inputted to the apparatus. FIG. 3 is identical to FIG. 1except that unused signal lines are indicated by dotted lines.Hereinafter, a description will be given of the operation of thewaveform equalization apparatus in the case where a 64-QAM signal isinputted to the apparatus, with reference to FIG. 3.

Initially, a control signal for switching the inputs to each of theselectors 107˜112 according to the QAM signal, for example, “0”, issupplied from the outside to the filter construction control terminal122, and a real component of a 64-QAM signal is inputted to the datainput terminal 1 while an imaginary component thereof is inputted to thedata input terminal 120.

In the TF unit 101 a, the TF 101 performs a filtering process on thereal component of the QAM signal which is inputted to the data inputterminal 1, and outputs the filter-processed signal to the adder 113,and outputs a delay signal to the TF 102. Further, the adder 118 outputsthe signal obtained by the addition to the tap coefficient control unit150.

The selector 109 selects the imaginary component of the QAM signalsupplied from the data input terminal 120, on the basis of the filterconstruction control signal, and outputs it to the TF unit 105 a. In theTF unit 105 a, the TF 105 performs a filtering process on the imaginarycomponent of the QAM signal, and outputs the filter-processed signal tothe adder 114, and outputs a delay signal to the TF 106. The TF 106 inthe TF unit 105 a performs a filtering process on this delay signal, andoutputs the filter-processed signal to the adder 114. Further, the delaysignal outputted from the TF 105 is inputted to the selector 111, as amain signal component of the TF unit 105 a. The adder 114 adds thefilter-processed signal from the TF 105 and the filter-processed signalfrom the TF 106, and outputs the sum to the adder 116.

The selector 108 selects the real component of the QAM signal which isinputted to the data input terminal 1, on the basis of the filterconstruction control signal, and outputs it to the TF 104. The TF 104outputs the filter-processed signal to the adder 136. The adder 116 addsthe filter-processed signal from the TF 104 and the output of the adder114, and outputs the sum to the adder 117. The selector 111 selects themain signal component of the TF unit 105 a, and outputs it to the adder117. The adder 117 adds the output of the adder 116 and the output ofthe selector 111, and outputs the result of the addition, as animaginary component of a waveform-equalized QAM signal, from the dataoutput terminal 121. Further, the adder 117 outputs the result of theaddition to the tap coefficient controller 150. The tap coefficientcontroller 150 calculates differences between a most reliable symbolvalue among the symbol values the QAM signal can take, and the output ofthe adder 118, the output of the adder 117, the outputs or therespective taps of the TF unit 101 a, and the outputs of the respectivetaps of the TF unit 105 a, and obtains tap coefficients to be used inthe TF 101˜TF 106 on the basis of the LMS algorithm, using thesedifferences, and transmits a control signal instructing updation of thetap coefficients to the TFs 101˜106, thereby updating the tapcoefficients.

In this way, as for the QAM signal having both of the real component andthe imaginary component, the TFs 101˜106 are connected as complexfilters by controlling the selectors 107˜112.

Generally, a TF having many taps is required for waveform equalizationof a VSB signal. On the other hand, plural TFs connected in parallel arerequired for complex operations in waveform equalization of a QAM signalalthough the number of taps in each TF may be smaller. Therefore, inthis first embodiment, the four TF units, i.e., the TF units 101 a, 103a, 104, and 105 a, are prepared in advance, and part of the four TFunits, i.e., the TF units 103 a, 104 a, and 105 a, are connected inseries to make a long TF having many taps when the input signal is a VSBsignal, while the four TF units are connected in parallel to realize afiltering process based on complex operations when the input signal is aQAM signal. Accordingly, the waveform equalization apparatus of thisfirst embodiment is adaptable to the waveform equalization processes forthe both signals, and delivers sufficient performances in the processesfor the respective signals.

Further, a TF is usually very large in circuit scale as compared withother circuits such as a selector and, therefore, it occupies thegreater part of a waveform equalization circuit. In the waveformequalization apparatus of the first embodiment, however, the input tothe filter construction control terminal 122 is varied between the casewhere the input signal is a VSB signal and the case where it is a QAMsignal, whereby the whole filter is constructed as a real componentfilter when the input signal is a VSB signal while it is constructed asa complex filter when the input signal is a QAM signal. Therefore, thewaveform equalization processes for the VSB signal and the QAM signalcan share the TFs, whereby both of the VSB signal and the QAM signal canbe waveform-equalized without increasing the number of TFs, resulting ina waveform equalization apparatus which can perform waveformequalization on the VSB signal and the QAM signal without increasing thecircuit scale.

Embodiment 2

FIG. 4 is a block diagram illustrating a waveform equalization apparatusaccording to a second embodiment of the present invention. In FIG. 4,the same reference numerals as those shown in FIG. 1 designate the sameor corresponding parts. The waveform equalization apparatus according tothe second embodiment is different from the waveform equalizationapparatus according to the first embodiment only in that a TF unit 401 aand a TF unit 405 a are provided instead of the TF unit 101 a and the TFunit 105 a, and one of delay signals outputted from TFs 401˜403 in theTF unit 401 a and one of delay signals outputted from TFs 405˜407 in theTF unit 405 a are selected by a selector 409 and a selector 410,respectively, and the delay signals so selected are used as main signalcomponents of the TF unit 401 a and the TF unit 405 a, respectively.

The TF unit 401 a is provided with 16-tap TFs 401˜404. The TF 401receives an input signal applied to the data input terminal 1, andoutputs a signal obtained by performing a filtering process on the inputsignal, to an adder 411, and outputs a delay signal thereof to the TF402 and a selector 409. The TF 402 receives the delay signal from the TF401, and outputs a signal obtained by a filtering process to the adder411, and outputs a delay signal to the TF 403 and the selector 409. TheTF 403 receives the delay signal from the TF 402, and outputs a signalobtained by a filtering process to the adder 411, and outputs a delaysignal to the TF 404 and the selector 409. The TF 404 receives the delaysignal from the TF 403, and outputs a signal obtained by a filteringprocess to the adder 411. The TF unit 401 a is equivalent to a 64-tapTF, and one of the delay signals outputted from the TFs 401˜403 to theselector 409 serves as a main signal component of the TF unit 401 a. Theselector 409 selects one of the delay signals supplied from the TFs401˜403, on the basis of a center tap control signal indicating a centertap position, which signal is supplied from a center tap controlterminal 413, and outputs the selected signal. In this secondembodiment, it is assumed that the delay signal from the TF 401 iselected when the center tap control signal is “0”, the delay signal fromthe TF 402 is selected when the center tap control signal is “1”, andthe delay signal from the TF 403 is selected when the center tap controlsignal is “2”. The center tap control signal is previously stored in anexternal register or the like (not shown), and it is supplied to thecenter tap control terminal 413 according to an instruction from anexternal controller or the like (not shown). The adder 411 sums thesignals which are outputted from the respective TFs 401˜404 as theresults of the filtering processes, and outputs the sum to the adder115.

The TF unit 405 a is provided with 16-tap TFs 405˜408. The TF 405receives the signal outputted from the selector 109, and outputs asignal obtained by performing a filtering process on the signal, to anadder 412, and outputs a delay signal thereof to the TF 406 and aselector 410. The TF 406 receives the delay signal from the TF 405, andoutputs a signal obtained by a filtering process to the adder 412, andoutputs a delay signal to the TF 407 and the selector 410. The TF 407receives the delay signal from the TF 406, and outputs a signal obtainedby a filtering process to the adder 412, and outputs a delay signal tothe TF 408 and the selector 410. The TF 408 receives the delay signalfrom the TF 407, and outputs a signal obtained by a filtering process tothe adder 412. The TF unit 405 a is equivalent to a 64-tap TF, and oneof the delay signals outputted from the TFs 405˜407 to the selector 410serves as a main signal component of the TF unit 405 a. The selector 410selects one of the delay signals supplied from the TFs 405˜407, on thebasis of the center tap control signal supplied from the center tapcontrol terminal 413. In this second embodiment, it is assumed that thedelay signal from the TF 405 is selected when the center tap controlsignal is “0”, the delay signal from the TF 406 is selected when thecenter tap control signal is “1”, and the delay signal from the TF 407is selected when the center tap control signal is “2”. The adder 412sums the signals which are outputted from the respective TFs 405˜408 asthe results of the filtering processes, and outputs the sum to the adder116.

FIG. 5 is a block diagram for explaining the operation of the waveformequalization apparatus according to the second embodiment in the casewhere a VSB signal is inputted to the apparatus. The waveformequalization apparatus shown in FIG. 5 is different from that shown inFIG. 4 only in that unused signal lines are indicated by dotted lines.Hereinafter, the operation of the waveform equalization apparatusaccording to the second embodiment in the case where a 8-VSB signal isinputted will be described with reference to FIG. 5. As for theoperations of the same constituents as those described for the firstembodiment, repeated description is not necessary.

When a 8-VSB signal is inputted to the data input terminal 1 while “1”is inputted to the filter construction control terminal 122, theselectors 107, 108, and 109 operate in the same manner as described forthe case where the VSB signal is inputted to the waveform equalizationapparatus of the first embodiment, whereby the TF unit 103 a, the TFunit 104 a, and the TF unit 405 a are connected in series. The TF 401 inthe TF unit 401 a performs a filtering process on the 8-VSB signalinputted to the data input terminal 1, outputs the filter-processedsignal to the adder 411, and outputs a delay signal to the TF 402, andfurther, outputs the delay signal to the selector 409. The TF 402 in theTF unit 401 a performs a filtering process on the delay signal suppliedfrom the TF 401, outputs the filter-processed signal to the adder 411,and outputs a delay signal to the TF 403, and further, outputs the delaysignal to the selector 409. The TF 403 in the TF unit 401 a performs afiltering process on the delay signal supplied from the TF 403, outputsthe filter-processed signal to the adder 411, and outputs a delay signalto the TF 404, and further, outputs the delay signal to the selector409. The TF 404 performs a filtering process on the delay signalsupplied from the TF 403, and outputs the filter-processed signal to theadder 411. The adder 411 sums the filter-processed signals obtained fromthe respective TFs 401˜404, and outputs the sum to the adder 115.

When “0” is inputted to the center tap control terminal 413, theselector 409 selects the delay signal from the TF 401 as a main signalcomponent of the TF unit 401 a, and outputs it. Therefore, the selector409 outputs data which is delayed by 16 symbols with respect to the datainputted from the data input terminal 1, and the center tap of the TF401 a, i.e., the tap for taking the main signal component, becomes the16th tap. Likewise, when “1” is inputted to the center tap controlterminal 413, the selector 409 selects the delay signal of the TF 402 asthe main signal of the TF unit 401 a and outputs it, whereby the centertap of the TF unit 401 a becomes the 32nd tap. Further, when “2” isinputted to the center tap control terminal 413, the selector 409selects the delay signal of the TF 403 as the main signal of the TF unit401 a, whereby the center tap of the TF unit 401 a becomes the 48th tap.In this way, the selector 409 receives the center tap control signalinputted to the center tap control terminal 413, and selects one of thedelay signals outputted from the respective TFs 401˜403, as the mainsignal of the TF unit 401 a, on the basis of the center tap controlsignal, and outputs the selected signal to the adder 118.

The TF 405 in the TF unit 405 a performs a filtering process on thedelay outplay of the TF 104, which is selected by the selector 109, andoutputs the filter-processed signal to the adder 412, and outputs adelay signal thereof to the TF 406. The TF 406 performs a filteringprocess on the delay signal supplied from the TF 405, and outputs thefilter-processed signal to the adder 412, and outputs a delay signal tothe TF 407. The TF 407 performs a filtering process on the delay signalsupplied from the TF 406, and outputs the filter-processed signal to theadder 412, and outputs a delay signal to the TF 408. The TF 408 performsa filtering process on the delay signal supplied from the TF 407, andoutputs the filter-processed signal to the adder 412. The adder 412 sumsthe filter-processed signals obtained from the respective TFs 405˜408,and outputs the sum to the adder 116.

The selector 110, the selector 111, and the selector 112 operate in thesame way as described for the case where the VSB signal is inputted tothe apparatus of the first embodiment, and a signal obtained by addingthe filter-processed outputs from the TF 401, TF 402, TF 403, TF 404, TF103, TF 104, TF 405, TF 406, TF 407, and TF 408 and the output from theselector 409 which is the main signal component of the TF unit 401 a, issupplied as the output of the adder 118 to the delay unit 4 and the dataoutput terminal 11. Thereby, the waveform-equalized VSB signal isoutputted from the data output terminal 11.

FIG. 6 is a block diagram for explaining the operation of the waveformequalization apparatus according to the second embodiment in the casewhere a QAM signal is inputted to the apparatus. The waveformequalization apparatus shown in FIG. 6 is identical to that shown inFIG. 4 except that unused signal lines are shown by dotted lines.Hereinafter, the operation of the waveform equalization apparatus in thecase where a 64-QAM signal is inputted to the apparatus will bedescribed with reference to FIG. 6. With respect to the sameconstituents as first embodiment, the operations thereof will not bedescribed repeatedly.

Initially, a real component of a 64-QAM signal is inputted to the datainput terminal 1 while an imaginary component thereof is inputted to thedata input terminal 120, and “0” is inputted to the filter constructioncontrol terminal 122. As in the above-described case for processing theVSB signal, the TF unit 401 a outputs the results of filtering processesperformed in the respective TFs 401˜404 to the adder 411, and outputsdelay outputs of the respective TFs 401˜403 to the selector 409. Theadder 411 sums the filter-processed signals obtained from the respectiveTFs 401˜404, and outputs the sum to the adder 115. Like the TF unit 401a, the TF unit 405 a outputs the results of filtering processesperformed by the respective TFs 405˜408 to the adder 412, and outputsdelay outputs of the respective TFs 405˜407 to the selector 410. Theadder 412 sums the filter-processed signals obtained by the respectiveTFs 405˜408, and outputs the sum to the adder 116.

At this time, as in the case where the VSB signal is inputted, theselector 409 selects one of the delay signals outputted from the TFs401˜403, as a main signal component of the TF unit 401 a, on the basisof the center tap control signal inputted to the center tap controlterminal 413, and outputs the selected delay signal to the adder 118.

Further, like the above-described selector 409, the selector 410 selectsone of the delay signals outputted from the TFs 405˜407, as a mainsignal component of the TF unit 405 a, on the basis of the center tapcontrol signal inputted to the center tap control terminal 413, andoutputs the selected delay signal to the selector 111.

For example, when the center tap control signal is “2”, the selector 409selects the delay signal from the TF 403 and outputs it, therebyoutputting data which is delayed by 48 with respect to the data inputtedfrom the data input terminal 1. At the same time, the selector 410selects the delay output of the TF 407 and outputs it, therebyoutputting data which is delayed by 48 with respect to the data inputtedfrom the data input terminal 120. Therefore, the center tap positions ofthe real component and the imaginary component become the 48th tap.Likewise, when “0” is inputted to the center tap control terminal 413,the center tap position becomes the 16th tap, and when “1” is inputtedto the center tap control terminal 413, the center tap position becomesthe 32nd tap. In this way, the center tap positions of the TF unit 401 aand the TF unit 405 a are controlled by the center tap control signal.

The selector 107, the selector 108, and the selector 109 operate in thesame manner as described for the case where a QAM signal is inputted tothe waveform equalization apparatus of the first embodiment shown inFIG. 3, whereby the TF unit 401 a, the TF unit 103 a, the TF unit 104 a,and the TF unit 405 a are connected as a complex filter. Further, theselector 110 and the selector 112 also operate in the same manner asdescribed for the case where a QAM signal is inputted to the waveformequalization apparatus of the first embodiment shown in FIG. 3, and theselector 111 selects the output of the selector 410 and supplies it tothe adder 117. Thereby, a signal, which is obtained by adding the signalobtained by the filtering processes in the TF unit 401 a and the TF unit103 a, and the output of the selector 409, i.e., the main signal part ofthe real component of the QAM signal, is supplied to the data outputterminal 11 as the output of the adder 118. Further, a signal, which isobtained by adding the signals obtained by the filtering processes inthe TF unit 401 a and the TF unit 405 a, and the output of the selector410, i.e., the main signal part of the imaginary component of the QAMsignal, is supplied to the data output terminal 121 as the output of theadder 117. Thereby, the real component of the waveform-equalized QAMsignal is outputted from the data output terminal 11, and the imaginarycomponent of the waveform-equalized QAM signal is outputted from thedata output terminal 121.

As described above, according to the second embodiment of the presentinvention, the center tap control signal designating the center tapposition is inputted to the center tap control terminal 413, whereby thecenter tap position can be varied easily, and the range of equalizationcan be varied, thereby providing a waveform equalization apparatus whichenables an optimum tap arrangement according to the condition of theinput signal, regardless of whether the input signal is a VSB signal ora QAM signal.

While in this second embodiment the selectable center tap positions arethe 16th tap, the 32nd tap, and the 48th tap, the center tap positionsmay be set at other taps than those mentioned above. Further, the numberof selectable center taps (center tap positions) is not restricted tothree, and at least two center taps may be selected. In this case, delaysignals are taken from two or more tap positions, and the selectorselects a delay signal from one of these tap positions on the basis of acenter tap control signal, whereby the same effects as described for thesecond embodiment are achieved.

For example, in the waveform equalization apparatus according to thesecond embodiment, two TF units each having n pieces of TFs (n: integerequal to or larger than 3), which TFs are connected such that the delayoutput from the m-th TF (1≦m≦n−1: m integer) is inputted to the (m+1)thTF, may be employed instead of the TF 401 a and the TF 405 a,respectively; two adders for adding the filter-processed outputs fromthe respective TFs of the respective TF units and outputting the sums tothe adder 115 and the adder 116, respectively, may be employed insteadof the adder 411 and the adder 412; and two selectors each receiving thedelay outputs from the 1st to (n−1)th TFs of each TF unit, and selectingone of the delay outputs on the basis of a center tap control signal maybe employed instead of the selector 409 and the selector 410. Also inthis case, the center tap position can be varied according to the centertap control signal, whereby the same effects as described for the secondembodiment are achieved.

Embodiment 3

FIG. 7 is a block diagram illustrating a waveform equalization apparatusaccording to a third embodiment of the present invention. In FIG. 7, thesame reference numerals as those shown in FIG. 1 designate the same orcorresponding parts. A TF unit 701 a is provided with 16-tap TFs 701 and702, and a 32-tap TF 703. The TF 701 receives an input signal applied tothe data input terminal 1, and outputs a signal which is obtained byperforming a filtering process on the input signal, to an adder 711, andfurther, outputs a delay signal to the TF 702 and the adder 118. The TF102 receives the delay signal from the TF 701, and outputs a signalobtained by performing a filtering process on the input signal to theadder 711, and outputs a delay signal to the TF 703. The TF 703 receivesthe delay signal from the TF 702, and outputs a signal obtained byperforming a filtering process on the input signal, to the adder 711.Further, an operation control signal is supplied from the outsidethrough a filter operation control terminal 715 to the TF 703, and theoperating state of the TF 703 is changed by the operation controlsignal. The adder 711 sums the results of filtering processes which areoutputted from the TFs 701˜703, and outputs the sum to the adder 115.

A TF unit 704 a is provided with 32-tap TFs 704 and 705. The TF 704receives the output from the selector 107, and outputs a signal which isobtained by performing a filtering process on the input signal, to anadder 712, and outputs a delay signal which is obtained by delaying theinput signal with an internal delay circuit, to the TF 705. The TF 705receives the delay signal from the TF 704, and outputs a signal obtainedby performing a filtering process on the input signal to the adder 712,and outputs a delay signal to the selector 108. The TF 705 is suppliedwith the operation control signal through the filter operation controlterminal 715, and the operating state of the TF 705 is changed accordingto the operation control signal. The adder 712 sums the results offiltering processes which are outputted from the TF 704 and the TF 705,and outputs the sum to the selector 110 and the code inverter 119.

A TF unit 706 a is provided with 32-tap TFs 706 and 707. The TF 706receives the output from the selector 108, and outputs a signal obtainedby performing a filtering process on the input signal, to an adder 713,and outputs a delay signal to the TF 707. The TF 707 receives the delaysignal from the TF 706, and outputs a signal obtained by performing afiltering process on the input signal to the adder 713, and outputs adelay signal to the selector 109. The TF 707 is supplied with theoperation control signal through the filter operation control terminal715, and the operating state of the TF 707 is changed according to theoperation control signal. The adder 713 sums the results of product-sumoperations which are outputted from the TF 706 and the TF 707, andoutputs the sum to the adder 116.

A TF unit 708 a is provided with 16-tap TFs 708 and 709, and a 32-tap TF710. The TF 708 receives the output from the selector 109, and outputs asignal obtained by performing a filtering process on the input signal toan adder 714, and outputs a delay signal to the TF 709 and the selector111. The TF 709 receives the delay signal from the TF 708, and outputs asignal obtained by performing a filtering process on the input signal tothe adder 714, and outputs a delay signal to the TF 710. The TF 710receives the delay signal from the TF 709, and outputs a signal obtainedperforming a filtering process on the input signal to the adder 714.Further, the TF 710 is supplied with the operation control signal fromthe outside through the filter operation control terminal 715, and theoperating state of the TF 710 is changed by the operation controlsignal. The adder 714 sums the results of filtering processes which areoutputted from the TFs 708˜710, and outputs the sum to the adder 116.

The operation control signal to be applied to the filter operationcontrol terminal 715 is previously stored in an external register or thelike (not shown), and it is inputted to the filter operation controlterminal 715 according to an instruction of an external controller orthe like (not shown). In this third embodiment, as the operation controlsignal, a signal for setting the TFs 703, 705, 707, and 710 in theiractive states is outputted when performing waveform equalization on theVSB signal, and a signal for setting these TFs in their halt states isoutputted when performing waveform equalization on the QAM signal.

In the waveform equalization apparatus according to this thirdembodiment, the TF units 701 a, 704 a, 706 a, and 708 a are employedinstead of the TF units employed in the waveform equalization apparatusdescribed for the first embodiment, and when a VSB signal is inputted tothe apparatus, “0” is applied to the filter operation control terminal715 as a signal for setting the TFs 703, 705, 707, and 701 in theiractive states, whereby each of the TF units 701 a, 704 a, 706 a, and 708a functions as a 64-tap TF, like each TF unit according to the firstembodiment. Furthermore, in this third embodiment, the same filterconstruction control signal as that employed for the first embodiment isapplied to the filter construction control terminal 122 when a VSBsignal is inputted to the apparatus. Therefore, when performing waveformequalization on the VSB signal in this third embodiment, the sameoperation as described for the case where waveform equalization isperformed on the VSB signal in the waveform equalization apparatusaccording to the first embodiment, which operation has been describedwith reference to FIG. 2, is carried out. Accordingly, it is notnecessary to repeatedly describe the specific operation of the waveformequalization apparatus of this third embodiment in the case where a VSBsignal is inputted to the apparatus.

FIG. 8 is a block diagram for explaining the operation of the waveformequalization apparatus according to the third embodiment in the casewhere a QAM signal is inputted to the apparatus. The waveformequalization apparatus shown in FIG. 8 is identical to that shown inFIG. 7 except that unused signal lines are shown by dotted lines.Hereinafter, the operation of the waveform equalization apparatus of thethird embodiment in the case where at 64-QAM signal is inputted, will bedescribed with reference to FIG. 8. With respect to the sameconstituents as those of the waveform equalization apparatus accordingto the first embodiment, the operations thereof will not be describedrepeatedly.

A real component of a 64-QAM signal is inputted to the data inputterminal 1 while an imaginary component thereof is inputted to the datainput terminal 120, and “0” is inputted to the filter constructioncontrol terminal 122. The selectors 107, 108, and 109 operate in thesame manner as described for the case where a QAM signal is inputted tothe waveform equalization apparatus of the first embodiment shown inFIG. 3, whereby the TF units 701 a, 704 a, 706 a, and 708 a areconnected as a complex filter. Further, the selectors 110 and 112 alsooperate in the same manner as described for the case where a QAM signalis inputted to the apparatus of the first embodiment. Further, theselector 111 selects the delay output of the TF 708 and supplies it tothe adder 117. Thereby, a signal obtained by adding the signals whichare filter-processed by the TF units 701 a and 704 a and the delayoutput of the 701 which is the real component of the QAM signals, isoutputted from the adder 118 to the data output terminal 11. Further, asignal obtained by adding the signals which are filter-processed by theTF units 706 a and 708 a and the delay output of the TF 708 which is themain signal part of the imaginary component of the QAM signal, isoutputted from the adder 117 to the data output terminal 121.

When processing the QAM signal, in the TF unit 701 a, 704 a, 706 a, and708 a, sufficient filter characteristics can be obtained in many caseseven when all of the taps in each TF unit are not used. In this case,for example, “1” is inputted to the filter operation control terminal715 as a signal for setting the TFs 703, 705, 707, and 710 in their haltstates, whereby the TFs 703, 705, 707, and 710 halt the operations, andoutput “0” as filter-processed signals. Therefore, each of the TF units701 a, 704 a, 706 a, and 708 a functions as a TF having a tap length of32 taps.

When a tap length longer than 32 taps is required in each of the TFunits 701 a, 704 a, 706 a, and 708 a for sufficient filtercharacteristics, the set values in an external register or the like maybe changed so that a signal “0” which sets these TF units in theiractive states is applied to the filter operation control terminal 715.

As described above, according to the third embodiment of the invention,the operating states of the TFs 703, 705, 707, and 710 are changed bychanging the input to the filter operation control terminal 715according to the input signal, whereby the tap length of each TF unit(i.e., the number of taps constituting each TF unit) can be switchedbetween 32 taps and 64 taps. Thereby, the filter characteristics of thewaveform equalization process can easily be changed byincreasing/decreasing the number of taps in each TF unit according tothe input signal, and power consumption of the waveform equalizationapparatus can be reduced by avoiding use of unnecessary TFs.

While in this third embodiment the selectable tap length is 32 taps or64 taps, the tap length is not restricted thereto. Further, while thecenter tap position is the position of the 16th tap, the center tapposition is not restricted thereto.

For example, in this third embodiment, TF units, each having n pieces ofTFs (n: integer equal to or larger than 2) which are connected such thata delay output from the m-th TF (1≦m≦n−1, m: integer) is inputted to the(m+1)th TF, may be provided instead of the TF 701 a and TF 708 a; TFunits, each having s pieces of TFs (s: integer equal to or larger than2) which are connected so that a delay output from the t-th TF (1≦t≦s−1,m: integer) is inputted to the (t+1)th TF, may be provided instead ofthe TF 701 a and TF 708 a; and the operating state of at least one TFamong the TFs constituting each TF unit may be switched between theactive state and the halt state according to the filter operationcontrol signal. Also in this case, the same effects as mentioned aboveare achieved.

Furthermore, in this third embodiment, at least one of the TF units 701a, 704 a, 706 a and 708 a may be replaced with a TF unit which isprovided with n pieces of TFs (n: integer equal to or larger than 2)which are connected such that a delay output of the m-th TF (1≦m≦n−1, m:integer) is inputted to the (m+1)th TF, and the operating state of atleast one TF among the TFs in this TF unit may be switched between theactive state and the halt state according to the filter operationcontrol signal.

Embodiment 4

FIG. 10 is a block diagram illustrating a waveform equalizationapparatus according to a fourth embodiment of the present invention. InFIG. 10, the same reference numerals as those shown in FIG. 1 designatethe same or corresponding parts. The waveform equalization apparatuscomprises a data input terminal 1 for receiving a VSB signal which is asignal having only a real component; a digital filter unit 15 forperforming a waveform equalization process on the data inputted from thedata input terminal 1; a data output terminal 11 for outputting the VSBsignal which is waveform-equalized by the digital filter unit 15; and atap coefficient controller 10 for calculating tap coefficients to beused in the digital filter unit 15 on the basis of the data obtainedfrom the digital filter unit 15, and outputting the tap coefficients tothe digital filter unit 15.

In the digital filter unit 15, a 32-tap TF 2 receives the signalinputted to the data input terminal 1, performs a product-sum operationon signals obtained from the internal 32 taps and tap coefficients givento the respective taps by the tap coefficient controller 10, and outputsthe result of the product-sum operation to an adder 9, as a signalobtained by a filtering process. Further, the 32-tap TF 2 outputs adelay signal which is obtained by delaying the input signal, to a 32-tapTF 3 and the adder 9. The TF 3 receives the delay signal outputted fromthe TF 2, and outputs a signal obtained by performing a filteringprocess on the input signal, to the adder 9. The TF 2 and TF 3 areequivalent to a 64 tap TF, and the delay signal outputted from the TF 2is inputted to the adder 9, as a signal of the center tap of the 64-tapTF, i.e., as a main signal component. A delay unit 4 delays the signaloutputted from the adder 9 by 32 symbols, and outputs the delayed signalto a slicer 5. The slicer 5 maps the output signal from the delay unit 4to a closest value among the eight values, and outputs the mappedsignal, thereby removing an influence of noise of the input signal onthe subsequent processes.

A 64-tap TF 6 receives the signal outputted from the slicer 5, andoutputs a signal obtained by performing a filtering process on the inputsignal to the adder 9, and outputs a delay signal to a 64-tap TF 7. TheTF 7 receives the delay signal outputted from the TF 6, and outputs asignal obtained by performing a filtering process on the input signal tothe adder 9, and outputs a delay signal to a 64-tap TF 8. The 64-tap TF8 receives the delay signal outputted from the TF 7, and outputs asignal obtained by performing filtering process on the input signal, tothe adder 9. In this fourth embodiment, the three TFs 6, 7, and 8connected in series are used as a 192-tap TF. Further, signals obtainedfrom the respective taps included in the TFs 6, 7, and 8 are outputtedto the tap coefficient controller 10. The adder 9 sums the results ofthe product-sum operations obtained from the TFs 2, 3, 6, 7, and 8, andoutputs a signal obtained by the summing, from the data output terminal11, as a waveform-equalized VSB signal and, further, outputs the signalto the tap coefficient controller 10 did the delay unit 4. The tapcoefficient controller 10 calculates tap coefficients corresponding tothe respective taps in the TFs 2, 3, 6, 7, and 8, on the basis of theoutput from the adder 9 and the outputs from the respective taps of theTFs 6, 7, and 8, and controls updation of tap coefficients using thecalculated tap coefficients.

Next, the operation of the waveform equalization apparatus will bedescribed with reference to FIG. 10. Initially, when a VSB signal isinputted to the data input terminal 1, the input signal is subjected toa filtering process for waveform equalization by the TF 2 and the TF 3on the basis of the tap coefficients which are set by the tapcoefficient controller 10, and the results of product-sum operationsperformed on the outputs from the internal taps of the TF 2 and the TF3, and a delay signal obtained by delaying the input signal with the TF2, are transmitted to the adder 9 as the result of the filteringprocess. The adder 9 sums the inputted signals, and outputs a signalobtained by the summing, as an output signal from the data outputterminal 11, and further, outputs the signal to the tap coefficientcontroller 10 and the delay unit 4. The delay unit 4 delays the signalsupplied from the adder 9 by 32 symbols, and outputs a delay signal soobtained to the slicer 5. The slicer 5 maps the output of the delay unit4 to a closest value among the eight values the VSB signal can take,thereby removing influence of noise of the signal on the subsequentprocesses. The TF 6, TF 7, and TF 8 successively perform filteringprocesses on the output of the slicer 5, and output the results to theadder 9. The tap coefficient controller 10 obtains differences betweenthe outputs from the respective taps in the TFs 6, 7, and 8 and a mostreliable symbol value among the eight symbol values the VSB signal cantake, and a difference between the output from the adder 9 and the mostreliable symbol value, and updates the tap coefficients of the TFs 3, 6,7, and 8 using these differences, on the basis of the LMS (Least MeanSquare) algorithm.

The tap coefficient controller 10 performs updation of tap coefficientsusing an algorithm represented by formula (6), as the LMS algorithm forperforming the n th updation (n: positive integer) of a tap coefficientCi of a tap i (i: positive integer) in the TF2 or TF3.Ci(n+1)−Ci(n)−α×en×di  (6)wherein α indicates a fixed constant step size which determines thecoefficient updation amount, en indicates an error in the output signal,di indicates data of the tap i, and −α×en×di indicates the coefficientupdation amount.

When the tap coefficients of the TFs 6, 7, and 8 are to be obtained, then-th updation (n: positive integer) of the tap coefficient Ci is carriedout according to formula (7) as follows, using data di′ which isinputted to the TFs 6, 7, and 8 through the slicer 5 and outputted fromeach tap of these TFs.Ci(n+1)−Ci(n)−α×en×di′  (7)wherein α indicates a fixed constant step size which determines thecoefficient updation amount, en indicates an error in the output signal,and −α×en×di′ indicates the coefficient updation amount. In formula (7),di′ is an estimated value which is obtained by mapping the data of theabove-mentioned di to a most reliable value among the eight values theVSB signal can take, and appropriate coefficient updation is realized byformula (7) using the di′.

In this fourth embodiment, when the tap coefficients of the TFs 6, 7,and 8 are to be obtained, updation of the tap coefficients of the TFs 6,7, and 8, is carried out on the basis of formula (7) using the data di′which is obtained from the respective taps of the TFs 6, 7, and 8 byinputting the signal that is octal-leveled by the slicer 5 into the TFs6, 7, and 8 successively. In the conventional technique, the data di,i.e., the output delay data which is not passed through the slicer, isrequired for obtaining the tap coefficients of the TFs 6, 7, and 8, andtherefore, a 192-delay unit is required. In this fourth embodiment,however, such 192-delay unit for holding the output signal forcoefficient calculation is not necessary. As a result, the delay unit ofa relatively large size can be removed, thereby providing a waveformequalization apparatus with significantly reduced cost.

Embodiment 5

FIG. 9 is a block diagram illustrating a waveform equalization apparatusaccording to a fifth embodiment of the present invention. In FIG. 9, thesame reference numerals as those shown in FIG. 10 designate the same orcorresponding parts.

With reference to FIG. 9, a mode input signal S901 for determiningwhether the waveform equalization apparatus is in a normal operationmode or a test mode is supplied from the outside to a mode inputterminal 901. This mode input signal S901 is previously stored in anexternal register or the like (not shown), and it is inputted to themode input terminal 901 according to an instruction from an externalcontroller or the like (not shown). A test signal generator 902generates an impulse signal S902 for test, and outputs it to an inputsignal selector 903. The input signal selector 903, which is disposedbetween the data input terminal 1 and a digital filter unit 35, selectseither the input signal inputted from the data input terminal 1 or theimpulse signal S902 generated by the test signal generator 902 on thebasis of the value of the mode input signal S901 inputted from the modeinput terminal 901, and outputs it as a selected signal S903. A tapcoefficient controller 904 performs updation of tap coefficients asdescribed for the third embodiment when it is in the normal operationmode, and halts the updation of tap coefficients when it is in the testmode, on the basis of the mode input signal S901 inputted from the modeinput terminal 901.

Next, the operation of the waveform equalization apparatus in the case aVSB signal is inputted to the apparatus, will be described.

Initially, the normal operation mode will be described. When “0” isinputted as the mode input signal S901 to the mode input terminal 901,the input signal selector 903 selects the octal VSB signal inputted tothe data input terminal 1, and outputs it as a selected signal S903. Thedigital filter unit 15 performs a filtering process on the selectedsignal S903 in the same manner as described for the fourth embodiment.The tap coefficient controller 904 adaptively updates the tapcoefficients of the digital filter unit 15 in the same manner asdescribed for the fourth embodiment, on the basis of the output signalfrom the data output terminal 11 and the outputs of the respective tapsin the TFs 6˜8.

Next, the case where the normal operation mode is changed to the testmode will be described. When the value of the mode input signal S901applied to the mode input terminal 901 is changed to “1”, the inputsignal selector 903 selects the impulse signal S902 outputted from thetest signal generator 902, and outputs it as a selected signal S903. Thedigital filter unit 15 performs a filtering process on the selectedsignal S903 in the same manner as described for the fourth embodiment.The tap to waveform equalization, with the same effects as describedabove.

1. A waveform equalization apparatus comprising: a first input terminalto which only a real component of a digital input signal to bewaveform-equalized is applied; a second input terminal to which only animaginary component of the digital input signal to be waveform-equalizedis applied; plural transversal filters for performing filteringprocesses for waveform equalization on the digital input signal; a firstoutput terminal from which only a real component of a waveform-equalizeddigital output signal is outputted; a second output terminal from whichonly an imaginary component of the waveform-equalized digital outputsignal is outputted; plural selectors for selecting a connection oflines which interconnect the first or second input terminal, the pluraltransversal filters, and the first or second output terminal; and afilter construction control signal generator for generating a filterconstruction control signal which controls the plural selectors tocontrol the filter construction such that the whole apparatus becomes areal component filter when the digital input signal is a signal havingonly a real component, and becomes a complex filter when the digitalinput signal is a signal having both a real component and an imaginarycomponent.
 2. The waveform equalization apparatus of claim 1, whereinthe same number of transversal filters among the plural transversalfilters are used when the whole apparatus becomes a real componentfilter as well as when the whole apparatus becomes a complex filter. 3.The waveform equalization apparatus of claim 1, wherein the signalhaving only the real component is a VSB signal, and the signal havingboth of the real component and the imaginary component is a QAM signal.4. The waveform equalization apparatus of claim 1, wherein apredetermined transversal filter among the plural transversal filtershas plural taps; and the waveform equalization apparatus furthercomprising: a tap selector for selecting one of the plural taps; and acenter tap control signal generator for generating a center tap controlsignal for changing the position of a center tap of the predeterminedtransversal filter, by controlling the tap selector.
 5. The waveformequalization apparatus of claim 1, wherein the tap length of apredetermined transversal filter among the plural transversal filters ischangeable according to a filter operation control signal; and thewaveform equalization apparatus further comprising a filter operationcontrol signal generator for generating a filter operation controlsignal which changes the filter operation by changing the tap length ofthe predetermined transversal filter.
 6. A waveform equalizationapparatus comprising a first input terminal to which a digital inputsignal having only a real component is inputted; a second input terminalto which a digital input signal having only an imaginary component isinputted; first and second output terminals; first to fourth transversalfilter (hereinafter referred to as TF) units for performing filteringprocesses for waveform equalization; a delay means for delaying an inputsignal to output a delayed signal; and first and second tap coefficientcontrol means for controlling tap coefficients of the first to fourth TFunits, wherein when a signal is applied to only the first inputterminal, the first to fourth TF units are connected as follows: thesignal applied to the first input terminal is inputted to the first TFunit; a signal which is obtained by delaying a signal outputted from thefirst output terminal with the delay means is inputted to the second TFunit; a delay output from the second TF unit is inputted to the third TFunit; a delay output from the third TF unit is inputted to the fourth TFunit; and signals which are filter-processed by the second to fourth TFunits are added to a signal which is filter-processed by the first TFunit and a main signal component of the first TF unit, and the result ofthe addition is outputted from the first output terminal; and waveformequalization is performed on the input signal to the first inputterminal while controlling the tap coefficients of the first to fourthTF units with the first tap coefficient control means on the basis ofthe output from the first output terminal, and a signal so obtained isoutputted from the first output terminal; and when signals are appliedto both of the first input terminal and the second input terminal, thefirst to fourth TF units are connected as follows: the signal applied tothe first input terminal is inputted to the first and third TF units;the signal applied to the second input terminal is inputted to thesecond and fourth TF units; the main signal component of the first TFunit is added to a value which is obtained by subtracting the signalfilter-processed by the second TF unit from the signal filter-processedby the first TF unit, and the result of the addition is outputted fromthe first data output terminal; and the signal filter-processed by thethird TF unit, the signal filter-processed by the fourth TF unit, andthe main signal component of the fourth TF unit are added, and theresult of the addition is outputted from the second output terminal; andthe input signals applied to the first and second input terminals aresubjected to waveform equalization while controlling the tapcoefficients of the first to fourth TF units with the second tapcoefficient control means on the basis of the outputs from the first andsecond output terminals, and the real component of the signal soobtained is outputted from the first output terminal while the imaginarycomponent of the signal so obtained is outputted from the second outputterminal.
 7. The waveform equalization apparatus of claim 6, whereineach of the first and fourth TF units is provided with n pieces of TFs(n: integer equal to or larger than 3), and the respective TFs areconnected such that a delay output from the m-th TF (1≦m≦n−1, m:integer) is inputted to the (m+1)th TF, and said waveform equalizationapparatus further including: a first selection means for receiving delayoutputs from the first to (n−1)th TFs of the first TF unit,respectively, selecting one of the plural delay outputs on the basis ofa center tap control signal that is supplied from the outside, andoutputting the selected signal as a main signal component of the firstTF unit; and a second selection means for receiving delay outputs fromthe first to (n−1)th TFs of the fourth TF unit, respectively, selectingone of the plural delay outputs on the basis of the center tap controlsignal, and outputting the selected delay output as a main signalcomponent of the fourth TF unit.
 8. The waveform equalization apparatusof claim 6, wherein at least one of the first to fourth TF units isprovided with n pieces of TFs (n: integer equal to or larger than 2),and the respective TFs are connected such that a delay output from them-th TF (1≦m≦n−1, m: integer) is inputted to the (m+1)th TF, and theoperating state of at least one of the TFs is switched between theactive state and the halt state by a filter operation control signalthat is supplied from the outside.
 9. The waveform equalizationapparatus of claim 6, wherein each of the first and fourth TF units isprovided with n pieces of TFs (n: integer equal to or larger than 2),and the respective TFs are connected such that a delay output from them-th TF (1≦m≦n−1, m: integer) is inputted to the (m+1)th TF; each of thesecond and third TF units is provided with s pieces of TFs (s: integerequal to or larger than 2), and the respective TFs are connected suchthat a delay output from the t-th TF (1≦t≦s−1, t: integer) is inputtedto the (t+1)th TF; and the operating state of at least one TF among theplural TFs constituting each of the first to fourth TF units is switchedbetween the active state and the halt state by a filter operationcontrol signal that is supplied from the outside.
 10. A waveformequalization apparatus comprising: a first input terminal to which adigital input signal having only a real component is applied; a secondinput terminal to which a digital input signal having only an imaginarycomponent is applied; a first TF unit for receiving the input signalapplied to the first input terminal, and outputting a signal which issubjected to a filtering process for waveform equalization, and a mainsignal component in the filtering process; a first selection circuithaving first and second inputs, receiving, as the second input, theinput signal applied to the second inputs terminal, and selecting eitherof the first and second inputs to output the selected input; a second TFunit for receiving the output of the first selection circuit, andoutputting a signal which is subjected to a filtering process forwaveform equalization, and a delay signal obtained by delaying the inputsignal; a second selector for selecting either the input signal appliedto the first input terminal or the delay signal outputted from thesecond TF unit, and outputting the selected signal; a third TF unit forreceiving the output of the second selection circuit, and outputting asignal which is subjected to a filtering process for waveformequalization, and a delay signal obtained by delaying the input signal;a third selector for selecting either the input signal applied to thesecond input terminal or the delay signal outputted from the third TFunit, and outputting the selected signal; a fourth TF unit for receivingthe output of the third selection circuit, and outputting a signal whichis subjected to a filtering process for waveform equalization, and amain signal component in the filtering process; a fourth selector forselecting either the signal obtained by the filtering process in thesecond TF unit or a signal obtained by inverting the filter-processedsignal, and outputting the selected signal; a fifth selector forselecting either a signal which is obtained by adding the output of thefourth selector and the signal obtained by the filtering process in thefirst TF unit, or the main signal component outputted from the fourth TFunit, and outputting the selected signal; a sixth selector for selectingeither a signal which is obtained by adding the output of the fourthselector and the signal obtained by the filtering process in the firstTF unit, or a signal which is obtained by adding the signal obtained bythe filtering process in the third TF unit and the signal obtained bythe filtering process in the fourth TF unit, and outputting the selectedsignal; a first output terminal for outputting a signal which isobtained by adding the output of the sixth selector and the main signalcomponent of the first TF unit; a delay unit for delaying a signal whichis obtained by adding the output of the sixth selector and the mainsignal component of the first TF unit, and outputting the delayed signalso that it becomes a first input to the first selector; a second outputterminal for outputting a signal which is obtained by adding the outputof the fifth selector, the signal obtained by the filtering process inthe third TF unit, and the signal obtained by the filtering process inthe fourth TF unit; a first tap coefficient control means forcontrolling the tap coefficients of the first to fourth TF units, on thebasis of a signal which is obtained by adding the output of the sixthselector and the main signal component of the first TF unit; and asecond tap coefficient control means for controlling the tapcoefficients of the first to fourth TF units, on the basis of the signalwhich is obtained by adding the output of the sixth selector and themain signal component of the first TF unit, as well as the signal whichis obtained by adding the output of the fifth selector, the signalobtained by the filtering process in the third TF unit, and the signalobtained by the filtering process in the fourth TF unit; wherein, when asignal is inputted to only the first input terminal, the first selectorselects the input from the delay unit and outputs it; the secondselector selects the delay signal from the second TF unit and outputsit; the third selector selects the delay signal from the third TF unitand outputs it; the fourth selector selects the signal which is obtainedby the filtering process in the second TF unit; and outputs it; thefifth selector selects the signal which is obtained by adding the outputof the fourth selector and the signal obtained by the filtering processin the first TF unit; and outputs it; the sixth selector selects thesignal which is obtained by adding the output of the fifth selector, thesignal obtained by the filtering process in the third TF unit, and thesignal obtained by the filtering process in the fourth TF unit, andoutputs it; and the first tap coefficient control means control the tapcoefficients of the first to fourth TF unit; and when signals areinputted to both of the first input terminal and the second inputterminal, the first selector selects the input of the second inputterminal and outputs it; the second selector selects the input of thefirst input terminal and outputs it; the third selector selects theinput of the second input terminal and outputs it; the fourth selectorselects an inverted signal of the signal which is obtained by thefiltering process in the second TF unit, and outputs it; the fifthselector selects the main signal component of the fourth TF unit andoutputs it; the sixth selector selects the signal which is obtained byadding the output of the fourth selector and the signal obtained by thefiltering process in the first TF unit, and output it; and the first tapcoefficient control means controls the tap coefficients of the first tofourth TF units.
 11. The waveform equalization apparatus of claim 10,wherein each of the first and fourth TF units is provided with n piecesof TFs (n: integer equal to or larger than 3), and the respective TFsare connected such that a delay output from the m-th TF (1≦m≦n−1, m:integer) is inputted to the (m+1)th TF, and a signal which is obtainedby adding the signals that are filter-processed by the respective TFs isoutputted as a filter-processed output from each of the first and fourthTF units; said waveform equalization apparatus further including: aseventh selection means for receiving delay outputs from the first to(n−1)th TFs of the first TF unit, respectively, selecting one of theplural delay outputs on the basis of a center tap control signal that issupplied from the outside, and outputting the selected signal as a mainsignal component of the first TF unit; and an eighth selection means forreceiving delay outputs from the first to (n−1)th TFs of the fourth TFunit, respectively, selecting one of the plural delay outputs on thebasis of the center tap control signal, and outputting the selectedsignal as a main signal component of the fourth TF unit.
 12. Thewaveform equalization apparatus of claim 10, wherein at least one of thefirst to fourth TF units is provided with n pieces of TFs (n: integerequal to or larger than 2), and the respective TFs are connected suchthat a delay output from the m-th TF (1≦m≦n−1, m: integer) is inputtedto the (m+1)th TF, and the operating state of at least one of the TFs isswitched between the active state and the halt state by a filteroperation control signal that is supplied from the outside.
 13. Thewaveform equalization apparatus of claim 10, wherein each of the firstand fourth TF units is provided with n pieces of TFs (n: integer equalto or larger than 2), and the respective TFs are connected such that adelay output from the m-th TF (1≦m≦n−1, m: integer) is inputted to the(m+1)th TF; each of the second and third TF units is provided with spieces of TFs are (s: integer equal to or larger than 2), and therespective TFs are connected such that a delay output from the t-th TF(1≦t≦s−1, t: integer) is inputted to the (t+1)th TF; and the operatingstate of at least one TF among the plural TFs constituting each of thefirst to fourth TF units is switched between the active state and thehalt state by a filter operation control signal that is supplied fromthe outside.
 14. A waveform equalization apparatus comprising; an inputterminal to which a digital input signal having only a real component isapplied; a first TF for performing a waveform equalization filteringprocess on the input signal applied to the input terminal; an adder forreceiving, as one of plural inputs, the filter-processed output from thefirst TF, and adding the inputted signals to output the result of theaddition; an output terminal for outputting the output of the adder; adelay unit for delaying the output of the adder, and outputting thedelayed signal; a slicer for slicing the output of the delay unit; asecond TF for performing a waveform equalization filtering process onthe output of the slicer, inputting the filter-processed signal to theadder, and outputting a delay output obtained by delaying the output ofthe slicer, and signals obtained from the respective taps; a third TFfor performing a waveform equalization filtering process on the delayoutput of the second TF, inputting the filter-processed signal to theadder, and outputting a delay output obtained by delaying the delayoutput of the second TF, and signals obtained from the respective taps;a fourth TF for performing a waveform equalization filtering process onthe delay output of the third TF, inputting the filter-processed signalto the adder, and outputting signals obtained from the respective taps;and a tap coefficient control means for controlling the tap coefficientsof the first to fourth TFs on the basis of the output of the adder, andthe signals obtained from the respective taps of the second to fourthTFs.
 15. A waveform equalization apparatus comprising: an input terminalto which a digital signal is applied; a test signal generator forgenerating a signal for test; an input signal selection means forselecting either the signal applied to the input terminal or the testsignal, on the basis of a mode input signal that is supplied from theoutside; a digital filter unit having at least one TF, and performing afiltering process for waveform equalization on the signal that isselected by the input signal selection means; an output terminal foroutputting the signal that is filter-processed by the digital filterunit; and a tap coefficient control means for updating the tapcoefficient of the TF in the digital filter unit on the basic of thesignal that is filter-processed by the digital filter unit when theinput signal selection means selects the signal applied to the inputsignal, and performing no updation of the tap coefficient when the inputsignal selection means selects the test signal.